Conventional color cathode ray tubes are constructed of several major components including a shadow mask, a flanged glass faceplate, and a glass funnel-like envelope which is a frit-sealed to the faceplate. The faceplate has a number of shadow mask support studs embedded in its flange and the mask assembly includes a corresponding number of springs. Each spring has an alignment hole in one end thereof for engagement with a faceplate stud.
When the tube has been assembled, the shadow mask is attached to the faceplate and securely fastened thereto by the engagement of the faceplate studs with the mask spring holes. Thus, the mask assembly can be removed from the faceplate by compressing the leaf springs and disengaging the studs from the holes.
In the production of cathode ray tubes, in the process of establishing a tricolored phosphor pattern on the faceplate inner surface, the faceplate is first coated with a photosensitized phosphor slurry, the mask is attached to the faceplate, and a source of actinic light is directed through the mask apertures. Those preselected areas of the phosphor coating which are thus exposed to the actinic light are rendered insoluble in water while the nonexposed areas remain soluble. During this exposure, the mask must be securely attached to the faceplate.
The next processing step is to remove the mask from the faceplate and treat the exposured faceplate surface with a solvent to wash away the soluble slurry from those areas of the mask which have not been exposed. The result is a faceplate covered with an array of phosphor elements which corresponds to the aperture array of the mask. Each faceplate is mated with a particular mask to insure that the pattern of apertures in the mask corresponds precisely to the phosphor pattern deposited on the rear surface of the faceplate.
This entire procedure must be repeated for each of the three colored phosphors. Obviously, the shadow mask must be inserted into the faceplate and removed therefrom several times during the processing of the faceplate. Because the mask is only seven mils thick, it is easily dented and mis-shapen by accidental bumping and mishandling. Should a shadow mask become bent or dented, it and its corresponding faceplate must be scrapped because even small dents can cause substantial misregistration between the phosphor pattern on the faceplate and the aperture pattern on the mask.
Instead of using a shadow mask for exposure of the phosphor slurry, a single photographic mask may be used for exposure of many faceplates. Such a photographic mask is disclosed in copending applications Ser. No. 535,614 filed Dec. 23, 1974 (now U.S. Pat. No. 3,975,198) and claimed in copending application Ser. No. 643,201 filed Nov. 21, 1975, both assigned to assignee of the present application.
It has in the past been common to have the masks inserted and removed from their respective faceplates manually. This manual insertion and removal of the mask is not only time consuming but gives rise to mishandling. In addition, since the faceplate is normally in a horizontal position with its phosphor coating surface facing upwardly during insertion and removal of the panel, it is possible for human hair, lint, etc. to fall onto the mask or onto the faceplate itself. Such undesirable elements tend to contaminate either the mask or the faceplate and can result in a subsequently rejected cathode ray tube.
To overcome the inherent difficulties of manual attachment of the aperture mask to the faceplate, it is desirable to have means for automatically effecting such attachment. While the likely benefits of automatic mask attachment have been long appreciated, few commercially practical apparatus for accomplishing it have been made. Part of the problem with effecting the automatic machine attachment of a mask to a faceplate arises because of the fact that each mask spring hole should be in precise registry with its mating faceplate stud before they may be properly engaged. However, the holes and studs for a particular mask faceplate pair are not precisely enough located on their respective supporting structures to permit a machine to perform a standard attachment maneuver and guarantee that each mask faceplate pair will be properly mated. This problem, in addition to the requirement that an automatic machine attachment device be fast enough to keep up with other cathode ray tube production equipment, has forestalled the use of such devices in commercial production applications.
U.S. Pat. No. 3,838,483, issued to Ronald S. Baranski and Leslie L. Baur and issued to the assignee of this application, discloses and claims apparatus and method for the automatic insertion of a cathode ray tube shadow mask into a mating front panel having a wraparound flange. The apparatus includes means for aligning the shadow mask such that the mask alignment holes in the springs are positioned at points which lie in a substantially horizontal hole reference plane with each hole positioned at a predetermined location, and means for engaging the panel studs and aligning the panel by means of the studs to a position where the studs are located at points which lie in a substantially horizontal stud reference plane and at a location within that plane which places each stud in vertical alignment with and at a predetermined distance above its corresponding mask alignment hole. With the shadow mask and its panel in position of alignment, the mask springs are compressed to permit insertion of the mask assembly into the panel, the mask is raised the predetermined distance between the hole reference plane and the stud reference plane, and the springs are released to permit engagement between each stud and its corresponding alignment hole.
The apparatus disclosed in the Baranski and Baur patent utilized the mask-spring holes to position the mask. This is cumbersome since the engaging instrumentality must get out of its own way to permit stud engagement in the spring hole. Additional mechanisms are required to permit the instrumentality to be removed without losing the reference position of the mask which the instrumentality determined.
The invention of the present application is believed to be most useful when applied to a unique tube having a flangeless faceplate. Such a tube is disclosed in U.S. Pat. No. 3,894,260, issued to the assignee of this application. The tube has a flangeless, curved glass faceplate, a concave inner surface of which receives a phosphor screen. The funnel portion of this unique tube has a convex curved seal land (that is, the seal land defines a convex curved plane) which matches and mates with the curvature of the concave inner surface of the faceplate. Since the faceplate is flangeless, the sealing interface between the funnel and faceplate is curved rather than planar as in conventional tubes.
The use of a flangeless faceplate poses new problems in automatically attaching the shadow or photographic mask to the faceplate. The apparatus and method of U.S. Pat. No. 3,838,483 for use with a flanged faceplate rely on the presence of the flange for attachment of the shadow mask to the faceplate and utilizes the spring holes for positioning the mask. The method of this invention overcomes the problems indicated above and permits the automatic attachment of a shadow or photographic mask to a flangeless faceplate.